This invention relates to a liquid crystal display device, and more particularly to a display including a super twisted nematic liquid crystal composition.
Conventional super-twisted nematic liquid crystal display devices often suffer from discrimination lines and fingerprints. In super twisted nematic liquid crystal display devices, the ratio d/p of layer thickness (d) to spiral pitch (p) of the liquid crystal material is related to the twist angle (.phi.) of the liquid crystal material.
Japanese Patent Laid-Open No. 62-194224 discloses the possible range of d/p for normal operation as: EQU .phi./360-1/4&lt;d/p&lt;.phi./360
for a display device which does not suffer from discrimination lines or fingerprints. However, the range of d/p is reduced to less than one-half of the range defined by the above formula due to the scattering of layer thickness (d) and the variation of spiral pitch (p) of the liquid crystal material when the display device is mass produced and due to fluctuation of d/p from changes in temperature and the like. In particular, the range of d/p is narrowed markedly as the twist angle (.phi.) of the liquid crystal material is increased. Accordingly, for practical mass production, the twist angle (.phi.) of liquid crystal material has a limit of about 230.degree..
It is desirable to add at least one compound having high dielectric anisotropy to reduce the threshold voltage. However, when at least one compound is included having the general formula ##STR8## wherein R.sub.5 and R.sub.7 are R-- or RO--, ##STR9## R.sub.6 is --CN or --F, ##STR10## and R.sub.8 is --F, or --CN if ##STR11## which have high dielectric anisotropy and are effective for reducing threshold voltage, domains tend to form and the liquid crystal material has an extremely narrow d/p range.
Accordingly, it is desirable to provide a liquid crystal display device which does not suffer from these shortcomings of the prior art displays.